Fibrous stiffener with barrier function for making composite parts, and composite parts using this stiffener

ABSTRACT

Fibrous stiffener ( 1 ) for making composite parts molded from an injected resin base, of the type comprising at least one layer ( 2 ) based on stiffening fibers, characterized in that the layer ( 2 ) is connected by sewing or stitching to an elastomer sheet ( 6 ) extending over one of the wide faces of the layer ( 2 ) and performing a barrier function for any resin injected on one side or the other side of this sheet ( 6 ), the said elastomer sheet ( 6 ) being associated with a non-woven material ( 7 ) on at least one of its faces, to improve the adhesion of a resin injected on this side of the sheet ( 6 ).

[0001] This invention relates to the technical domain of production ofmaterials or composite parts that may or may not be conformed and thatcan be used directly or after transformation or association,particularly to form shaped structures or articles required in very manyapplications. More precisely, the purpose of the invention is a fibrousstiffener for making composite parts, that acts as a barrier forinjected resins, and composite parts comprising such a stiffener.

[0002] Composite parts according to prior art usually combine at leastone additional reinforcement, usually made of a textile or similarmaterial, with a resin matrix usually of the thermosetting type, inwhich the said reinforcement is embedded so that it is present eitherwithin the thickness of the formed part or at the surface, in order tocombine light weight with an acceptable mechanical strength.

[0003] It can be considered that these techniques are well controlledand are satisfactory in most applications. In other cases, it isdesirable to have thick stiffeners required in some applications, forexample plane or formed parts such as bodywork elements, pleasure boats,tanks or even aircraft. It has also been proposed that textilereinforcements like that described in patent FR 2 646 442 or in patentFR 2 734 847 could be used.

[0004] It is increasingly important to have simple and low costtechniques for making preforms for thick and lightweight walls or forlarge and lightweight bodies. When this type of preform is beingdesigned, a thermosetting resin is injected in the liquid state adjacentto the stiffener arranged with the required form. Therefore it isessential to have a stiffener which, due to its nature, prevents themigration of resin through the stiffener before the resin polymerizes.

[0005] Furthermore, it is frequently desirable to inject differentnatures of resin on each side of the stiffener. For example, it isnecessary to inject a resin such as a foaming resin in the centralposition of the composite part, to give the composite part the requiredvolume while remaining light weight, and another resin performing amechanizing function around the periphery in order to consolidate itsexternal walls.

[0006] In general, it is necessary to make a first core in a firstmould, for example by injecting polyurethane resin. This polyurethanecore must then be sanded to make it adhesive, knowing that after thepolyurethane surface has been molded its surface condition is smooth,after wax has been deposited. Finally, this polyurethane core is placedin a second mould with the textile stiffener to inject the second resin.

[0007] Therefore, it is usually necessary to make a preform composed ofthe polyurethane core associated with the fibrous stiffener used for thesecond injection. Therefore, composite parts are made in two moldingsteps with two slightly modified moulds, one for the first injection andthe other for the second injection.

[0008] In this context, one of the purposes of the invention is toprovide a sufficiently leak tight stiffening product to perform abarrier function between the two media on each side of this barrier, tomaintain their integrity. The leak tightness objective may be related toconfinement in the two media or once again to the need to controlmigration of a coating or decoration product that can be applied to oneof the faces of the final composite part or the stiffener. Inparticular, this type of stiffener can be used to make molded parts in asingle step.

[0009] The purpose of this invention is to satisfy this requirement bysuggesting improvements to textile stiffeners, such that thesestiffeners can perform a second barrier function for the injectedresin(s) and possibly for a coating or decoration product that can beapplied to the composite part or directly onto one of the wide stiffenerfaces.

[0010] The stiffener according to the invention must also haveappropriate surface properties to enable bonding of subsequentlyinjected resins.

[0011] In order to achieve these objectives according to the invention,the fibrous stiffener for making composite parts molded from an injectedresin base comprises at least one layer based on stiffening fibers. Thesaid layer is connected by sewing or stitching to an elastomer sheetextending over one of the wide faces of the layer and performing abarrier function for any resin injected on one side or the other side ofthis sheet, the said elastomer sheet being associated with a non-wovenmaterial on at least one of its faces to improve the adhesion of a resininjected on this side of the sheet.

[0012] Another purpose of the invention is a composite part obtainedfrom a fibrous stiffener according to the invention and at least twothermosetting or thermoplastic resin matrices each confined on each sideof the fibrous stiffener.

[0013] Various other characteristics can be determined from thefollowing description with reference to the attached drawings that showembodiments and means of implementation of the subject of the invention,as non-limitative examples.

[0014]FIG. 1 is a partly exposed perspective view illustrating a firstembodiment of the fibrous stiffener according to the invention.

[0015]FIG. 2 is a partial transverse section-elevation at a larger scaleof the fibrous stiffener according to FIG. 1.

[0016]FIG. 3 is a partial transverse section-elevation conform with FIG.2 illustrating another variant embodiment of the subject of theinvention.

[0017]FIG. 4 is a partial section at a different scale of a compositepart obtained from a fibrous stiffener according to the invention.

[0018] The invention relates to a fibrous stiffener specifically with aleak tightness function for making composite parts that may or may notbe molded, based on an injected thermosetting resin, such that thisfibrous stiffener forms a textile type additional reinforcement, atleast partly embedded in a resin matrix and particularly a thermosettingor thermoplastic resin.

[0019] One embodiment of the fibrous stiffener according to theinvention denoted as a whole by reference 1 is illustrated in FIG. 1 and2.

[0020] This type of stiffener comprises a layer 2 based on stiffeningfibers, essentially with an additional reinforcement characterized by asignificant thickness. Note that the invention is equally applicable tothin additional reinforcement, and consequently the embodiment shown inFIG. 1 is only given as an example.

[0021] In this example, the layer 2 is composed essentially of a core 3based on appropriate fibers. Preferably but not limitatively, thesefibers were crimped to reduce the weight and thickness characteristicsto the core 3, and to create an aerated texture. In one example, thecore 3 may be composed of polyester or polypropylene fibers with a titerequal to at least 30 decitex (dtex), a cut length of between 40 and 110mm that have previously being formed under the layer to apply atexturing treatment to give them a permanent crimping effect.

[0022] As shown in FIG. 1 and 2, the core 3 is advantageously used witha textile stiffener layer such as layer 4, on one of its faces forexample 3 ₂. The stiffener layer 4 may advantageously be composed offibrous layers such as glass and/or carbon and/or aramide fiber layers,smooth or two directional layers, or adjacent or contiguous or spacedthreads made of glass, carbon or aramide. Note that the layer 2 may alsobe composed of several cores 3 or materials with a resin creep ordrainage function, and layers 4, and that in most cases thedeformability and flexibility capability of this layer 2 makes itcapable of matching various conformations.

[0023] The fibrous stiffener according to the invention also comprisesan elastomer sheet 6 on one of the faces of the layer 2 that willperform a barrier function such that a thermosetting resin matrixinjected with the stiffener on one of the two sides remains confined onthis side, its migration being prevented by the flexible elastomer sheet6. As shown on FIGS. 1 and 2, the core 3 is associated with the textilestiffener layer 4 on one of its faces 3 ₂, and with the elastomer sheet6 on its other face 3 ₁.

[0024] This elastomer sheet 6 is made from a flexible, deformable andelastic material. For example, a natural rubber or a synthetic orartificial rubber sheet such as styrene butadiene rubber (SBR),chloroprene rubber, nitrile butadiene rubber (NBR) or isoprene rubber(IR) may be used. The sheet 6 advantageously and independently has athickness of between 0.15 to 0.5 mm, a density of 0.9 to 1.25, a stressmodulus of 0.15 to 2 MPa, preferably greater than or equal to 0.5 MPafor 100% deformation and elongation at failure equal to 50 to 600%, andpreferably greater than or equal to 400%. A 0.3 to 0.4 mm thick naturalrubber sheet with a density of 1.1 and with a stress modulus of 1.1 MPafor 100% deformation and an elongation at failure of greater than 600%are particularly suitable for this invention.

[0025] Furthermore, this sheet 6 is treated on at least one of its facesand preferably on its face 6 ₁ on the opposite side of layer 2, toimprove adhesion of any subsequently injected resin when the molded partis designed. This treatment consists of associating the face 6 ₁ of theelastomer sheet with a non-woven material 7.

[0026] Advantageously, as shown in FIG. 3, the face 6 ₂ on the same sideof the layer 2 as the elastomer sheet 6, may also be treated to improveadhesion of a resin injected on this side of the elastomer sheet 6. Onthis side, bond of the resin is already facilitated by the presence ofthe layer 2. In this case, the elastomer sheet 6 is advantageouslyassociated with a non-woven material 7 on its face 6 ₁ and with anothernon-woven material 8 on its face 6 ₂. For example, the non-wovenmaterials 7 and 8 are arranged on the faces of the elastomer sheet 6when the elastomer sheet is made. In particular, the bond may be made bythermo compression.

[0027] Non-woven materials 7 and 8 preferably have a porosity chosen asa function of the nature and the viscosity of the resins in theinjection state that will be used during manufacture of subsequentmolded part. Non-woven materials 7 and 8 are preferably but notexclusively based on fibers of the same nature and particularlymechanically bonded short fibers. According to one particularembodiment, the non-woven material 7 and if applicable the non-wovenmaterial 8 are based on polyethylene terephthalate or acrylic fiberswith a titer of between 0.5 and 6.7 decitex and a surface density of 20to 100 g/m².

[0028] Therefore, it can be seen that the fibrous stiffener 1 accordingto the invention is composed of several layers. The cohesion of thestiffener 1 is made by sewing-stitching. This sewing-stitching is ameans of connecting the layer 2 with the elastomer sheet 6 associatedwith one or two non-woven materials 7 and 8. In general,sewing-stitching 5 is used to connect the stiffener layer 4 to the core3 to form the layer 2 and to bond this layer 2 to the elastomer sheet 6.For example, this sewing-stitching may be made using a synthetic thread.

[0029] Therefore, it can be seen that the presence of the elastomersheet 6 is an essential characteristic of the invention. Even aftersewing-stitching, this sheet 6 must perform its leak tightness barrierfunction. The elastomer sheet 6, due to its flexibility and elasticity,tightens around the sewing-stitching thread after the needle has passedthrough it to make the seal. The function of the sheet 6 is to opposethe migration of the thermoplastic or thermosetting resin that isinjected in the liquid or paste state, when the molded parts are beingdesigned. Thus, before polymerization is complete and/or before theresin has been set, the resin remains confined on each side of theelastomer sheet 6.

[0030] Therefore the fibrous stiffener according to the invention isboth flexible, deformable and leak tight. Thus, it is perfectly suitablefor making preforms or molded composite parts. Its purpose is to form anadditional reinforcement for such a composite part that is obtainedprincipally by the injection of one or several resins, and particularlythermoplastic or thermosetting resins, and not necessarily by moldingand conformation.

[0031] This invention also relates to molded composite parts composed atleast partly of a fibrous stiffener according to the invention, combinedwith at least two thermosetting resin matrices confined on each side ofthe elastomer sheet. This type of molded part is shown partially in FIG.4. Two resins 9 and 10 are injected on each side of the fibrousstiffener 1. Advantageously, a composite part according to the inventionis at least partly composed of a first matrix 9 made of a thermosettingresin, for example vinylester, polyester or epoxy or phenolic resin, ora thermoplastic resin located at least partly in the fibrous layer andseparated by the elastomer sheet 6 from a second polyurethane matrix 10.

[0032] The thermoplastic or thermosetting resins are injected in theliquid or paste state on each side of the fibrous stiffener 1 accordingto the invention. The resin 9 injected into the layer 2 forms a matrixfor the fibers of this layer that is incorporated inside the thicknessof the resin wall. Before polymerization begins, the elastomer sheet 6acts as a leak tight barrier and therefore no migration of the resin cantake place to the other side of the stiffener. It thus becomes easy andpractical to make conform lightweight bodies or lightweight infillbodies or masses, at an attractive cost.

[0033] The polyester type resin 9 is usually injected on the side of thefibrous stiffener in order to form a reinforced wall. The polyurethaneresin 10 is injected on the other side and after stiffening, forms thevolume of the composite part although remaining lightweight.

[0034] In the injection state, the thermosetting resin 10 formed frompolyurethane bonds with difficulty onto the elastomer sheet and this iswhy it is preferable if the face 61 on the polyurethane side of thesheet 6 is associated with a non-woven material 9. On the other hand, inthe injection state, the resin 9 formed by a thermosetting polyesterresin or a thermoplastic resin adheres more easily to the elastomersheet 6, such that the non-woven material 8 can be eliminated.

[0035] These composite parts and preforms are made using conventionaltechniques well known to an expert in the subject.

[0036] The fibrous stiffeners 1 and the composite parts according to theinvention may be used to make boat structures such as covers, doors,rudder blades, rudders, bossing plates, portal frames, for makingvehicle structures such as trunk doors, tailgates or rear view mirrorsand industrial parts or sports and leisure articles, or wind generatorblades.

[0037] This invention is not limited to the examples described andillustrated, and various modifications can be made to it without goingoutside its scope.

1- Fibrous stiffener (1) for making composite parts molded from aninjected resin base (9, 10), of the type comprising at least one layer(2) based on stiffening fibers, characterized in that the layer (2) isconnected by sewing or stitching to an elastomer sheet (6) extendingover one of the wide faces of the layer (2) and performing a barrierfunction for any resin (9, 10) injected on one side or the other side ofthis sheet (6), the said elastomer sheet (6) being associated with anon-woven material (7, 8), on at least one of its faces (6 ₁, 6 ₂), toimprove the adhesion of a resin (9, 10) injected on this side of thesheet (6). 2- Fibrous stiffener (1) according to claim 1, characterizedin that the elastomer sheet (6) is associated with a non-woven material(7), at least on its face (6 ₁) opposite the layer (2). 3- Fibrousstiffener (1) according to claim 1 or 2, characterized in that theelastomer sheet (6) is associated with a non-woven material (7 and 8),on each of its faces (6 ₁ and 6 ₂), to improve adhesion of a resin (9,10) injected on each side of the sheet (6). 4- Fibrous stiffener (1)according to one of claims 1 to 3, characterized in that the elastomersheet (6) is made of a natural rubber or a synthetic rubber. 5- Fibrousstiffener (1) according to one of claims 1 to 4, characterized in thatthe porosity of the non-woven material (7, 8) is chosen as a function ofthe nature and the viscosity of the injected resin (9, 10). 6- Fibrousstiffener (1) according to claim 5, characterized in that the non-wovenmaterial (7, 8) is based on polyethylene terephthalate or acrylic fiberswith a titer of between 0.5 and 6.7 dtex and has a surface density of 20to 100 g/m². 7- Molded composite part obtained from a fibrous stiffener(1) according to one of claims 1 to 6, and at least two thermoplastic orthermosetting resin matrices (9, 10) each confined on each side of theelastomer sheet (6). 8- Composite part according to claim 7,characterized in that it is obtained from a first matrix (9) made ofpolyester, vinylester, epoxy or phenolic resin located at least partlyin the layer (2) and separated by the elastomer sheet (6) from a secondpolyurethane matrix (10). 9- Use of a fibrous stiffener (1) according toone of claims 1 to 6 or a composite part according to claim 7 or 8 tomake boat structures such as covers, doors, rudder blades, rudders,bossing plates, portal frames, for making vehicle structures such astrunk doors, tailgates or rear view mirrors, or industrial parts orsports and leisure articles, or wind generator blades.